Phosphating operation

ABSTRACT

Operational problems such as scale and sludge formation which are encountered in phosphating processes using compositions containing zinc and at least one of Ni, Co, or Zn may be alleviated by maintaining an effective level of dissolved iron cations in such compositions.

This application is the US National Phase application of and claimspriority from International Application Number PCT/US01/19499, filedJun. 18, 2001, which was published under PCT Article 21(2) in English onDec. 20, 2001, as WO 01/96627 A1. This application also claims priorityfrom US provisional application Ser. No. 60/212,205, filed Jun. 16,2000, which priority was also claimed in said International Application.

BACKGROUND OF THE INVENTION

This invention relates to the well known general field of phosphateconversion coating of metals and more particularly to phosphate coatingsformed from a liquid phosphating composition that contains both zinc andat least one of nickel, cobalt, and manganese as layer forming cations.The coatings formed from such a phosphating composition normally containboth zinc and at least the one(s) of nickel, cobalt, and zinc alsopresent in the phosphating compositions. These coatings may also containiron, particularly if a ferriferous substrate such as ordinary(non-stainless) steel is being phosphated.

Almost all phosphating compositions and processes are subject to theformation of “sludge”, a solid phase that separates spontaneously fromthe liquid phosphating composition as the latter is used. The majorcomponents of sludge are water-insoluble phosphates, usually of more orless the same type(s) that constitute the desired conversion coating.Although some attempts have been made to re-use sludge, in mostcommercial operations it still represents an economically significantcost of phosphating, because the anions and cations incorporated intothe sludge generally must be replenished along with the ions from thephosphating composition that actually form the desired phosphateconversion coating. Sludge generally either sinks to the bottom of anycontainer in which it forms or floats on the liquid phosphatingcomposition from which it forms and therefore can be easily removed fromthe liquid phosphating composition by filtering or skimming if desiredor needed. Sludge also is usually only weakly adherent to metalsurfaces, and if it does accumulate on them can be readily removed bybrushing, water flush, or the like.

A phenomenon less common than sludging that is sometimes observed incommercial phosphating is the formation of an adherent scale on processequipment, such as squeegee rolls, immersion heaters and heatexchangers, that must be kept in contact with the phosphatingcompositions during their use in order to maintain optimum conditionsfor phosphating. No phosphate conversion coating of these items ofprocess equipment is desired, and the objects are generally made ofnon-metals such as rubber for squeegee rolls or of metals such asstainless steel on which normal phosphate conversion coatings do notspontaneously form. Nevertheless, when these objects, especially iftheir surfaces are hot, are maintained in contact with liquidphosphating compositions for extended periods of time, a relativelyhard, adherent, and difficult to remove scale develops over the part ofthe surface in contact with the phosphating composition. Such scale isusually a heat insulator, so that even a relatively thin coating of thescale substantially impedes the heat transfer, between the metal and thephosphating compositions, that is a major reason for maintaining many ofthe metal surfaces in contact with the phosphating composition in thefirst place. On some other surfaces, such as squeegee rolls, the scalecan interfere with the intended operation of the process equipment inother ways. The scale must therefore be periodically removed, often asmuch as every few hours of operation, and scale must usually be removedprimarily by hand labor. Its removal therefore is often very costly.

In many commercial phosphating operations, particularly continuousoperations such as those usually used to phosphate large metal coils,there is a large fixed capital cost of the equipment used for thephosphating, so that it is economically important to obtain thephosphate coatings rapidly, thereby diminishing the fixed cost per itemof production by distributing this cost over more items. In mostinstances, phosphating reactions proceed more rapidly at higher ratherthan lower temperatures. A high phosphating temperature is thereforedesirable to minimize fixed costs per production item, but if the hightemperature causes more rapid scaling as it usually does when thephosphating composition used has a tendency to form scale, the cost ofscale removal may destroy the economic benefit of faster phosphating.

Phosphating compositions with a high total concentration of cations ofdivalent nickel, divalent cobalt, and/or divalent manganese (these threetypes of cations being hereinafter usually jointly referred to as “NCM”)along with zinc, as taught in U.S. Pat. No. 4,681,641 of Jul. 21, 1987to Zurilla et al., often provide better corrosion resistance to themetal substrates covered with them than do almost any other kind ofcommonly used phosphating. However, they are also more prone to sludgingand, when the total NCM content is very high, are much more prone toscaling than almost any other type of commonly used phosphating process.

Accordingly, a major object of this invention is to provide high NCMphosphating compositions and/or processes that produce less sludgeand/or scaling than previously used high NCM phosphating, particularlywhen the processes are operated at high temperatures.

Except in the claims and the operating examples, or where otherwiseexpressly indicated, all numerical quantities in this descriptionindicating amounts of material or conditions of reaction and/or use areto be understood as modified by the word “about” in describing thebroadest scope of the invention. Practice within the numerical limitsstated is generally preferred. Also, throughout this description, unlessexpressly stated to the contrary: percent, “parts of”, and ratio valuesare by weight; the term “polymer” includes “oligomer”, “copolymer”,“terpolymer”, and the like; the description of a group or class ofmaterials as suitable or preferred for a given purpose in connectionwith the invention implies that mixtures of any two or more of themembers of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the descriptionor of generation in situ by chemical reactions specified in thedescription, and does not necessarily preclude other chemicalinteractions among the constituents of a mixture once mixed;specification of materials in ionic form additionally implies thepresence of sufficient counterions to produce electrical neutrality forthe composition as a whole (any counterions thus implicitly specifiedshould preferably be selected from among other constituents explicitlyspecified in ionic form, to the extent possible; otherwise suchcounterions may be freely selected, except for avoiding counterions thatact adversely to the objects of the invention); the term “paint” and allof its grammatical variations are intended to include any similar morespecialized terms, such as “lacquer”, “varnish”, “electrophoreticpaint”, “top coat”, “color coat”, “radiation curable coating”, or thelike and their grammatical variations; and the term “mole” and itsgrammatical variations may be applied to elemental, ionic, and any otherchemical species defined by number and type of atoms present, as well asto compounds with well defined molecules.

BRIEF SUMMARY OF THE INVENTION

It has surprisingly been found that the presence of iron cations(particularly ferric cations) in an otherwise conventional high NCM zincphosphating composition reduces the formation of scale and/or sludge,even when the phosphating composition is maintained at a hightemperature.

Embodiments of the invention include working aqueous liquid compositionssuitable for contacting directly with metal surfaces to provideconversion coatings thereon; liquid or solid concentrates that will formsuch working aqueous liquid compositions upon dilution with water,optionally with addition of other ingredients; processes of usingworking aqueous liquid compositions according to the invention asdefined above to form protective coatings on metal surfaces and,optionally, to further process the metal objects with surfaces soprotected; protective solid coatings on metal surfaces formed in such aprocess, and metal articles bearing such a protective coating.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

A working composition according to the invention preferably compriseswater and the following components:

-   (A) dissolved phosphate anions;-   (B) dissolved NCM cations;-   (C) dissolved zinc cations; and-   (D) dissolved iron cations.    One or more of undissolved iron cations and the following components    may also be present in the working composition:-   (E) a phosphating accelerator that is not part of any of    components (A) through (D) as recited immediately above;-   (F) dissolved fluoride ions that are not part of any of    components (A) through (E) as recited immediately above;-   (G) an acidity adjustment agent that is not part of any of    components (A) through (F) as recited immediately above; and-   (H) sludge conditioner that is not part of any of components (A)    through (G) as recited immediately above.

In a composition according to the invention, component (A) preferably,at least for economy, is sourced to a composition according to theinvention by at least one of orthophosphoric acid and its salts of anydegree of neutralization. Component (A) can also be sourced to acomposition according to the invention by pyrophosphate and other morehighly condensed phosphates, including metaphosphates, which tend at thepreferred concentrations for at least working compositions according tothe invention to hydrolyze to orthophosphates. However, inasmuch as thecondensed phosphates are usually at least as expensive asorthophosphates, there is little practical incentive to use condensedphosphates, except possibly to prepare extremely highly concentratedliquid compositions according to the invention, in which condensedphosphates may be more soluble.

Whatever its source, the concentration of component (A) in a workingcomposition according to the invention, measured as its stoichiometricequivalent as PO₄ ⁻³ anions with the stoichiometry based on equalnumbers of phosphorus atoms, preferably is at least, with increasingpreference in the order given, 0.2, 0.4, 0.6, 0.70, 0.75, 0.80, 0.84,0.86, 0.88, 0.90, or 0.92% and independently preferably is not morethan, with increasing preference in the order given, 20, 10, 6.5, 5.0,4.0, 3.5, 3.0, 2.0, 1.8, 1.6, or 1.4%.

Component (B) of dissolved NCM cations is preferably sourced to thecomposition as at least one nitrate or phosphate salt (which may ofcourse be prepared by dissolving the elemental metal and/or an oxide orcarbonate thereof in acid), although any other sufficiently soluble saltof the NCM cations may be used. The entire NCM cations content of anywater-soluble NCM salt dissolved in a composition according to theinvention is presumed to be NCM cations in solution, irrespective of anycoordinate complex formation or other physical or chemical bonding ofthe NCM cations with other constituents of the composition according tothe invention. Independently of their source, the concentration of NCMcations in a working composition according to the invention preferablyis at least, with increasing preference in the order given, 0.4, 0.6,0.8, 0.10, 0.12, 0.14, 0.16, 0.18, or 0.20% and independently preferablyis not more than, with increasing preference in the order given, 1.5,1.0, 0.8, 0.70, 0.60, 0.55, 0.50, or 0.47%. If the concentration of NCMis too low, the improved corrosion resistance associated with a “highNCM” phosphating composition will not usually be achieved, while if thisconcentration is too high, the cost of the composition will increaseinordinately without any corresponding increase in performance. Amongthe NCM cations, nickel is most preferred because it is at leastslightly more effective in imparting high alkaline corrosion resistancethan cobalt or manganese.

Zinc cations for component (C) are preferably sourced to a compositionaccording to the invention from at least one zinc phosphate salt, atleast one zinc nitrate salt, and/or by dissolving at least one ofmetallic zinc, zinc oxide, and zinc carbonate in a precursor compositionthat contains at least enough phosphoric and/or nitric acid to convertthe zinc content of the oxide to a dissolved zinc salt. However, thesepreferences are primarily for economy and availability of commercialmaterials free from amounts of impurities that adversely affectphosphating reactions, so that any other suitable source of dissolvedzinc cations could also be used. As for NCM, the entire zinc content ofany salt or other compound dissolved or reacted with acid in acomposition according to the invention is to be presumed to be presentas cations when determining whether the concentration of zinc cationssatisfies a concentration preference as noted below.

In any working composition according to the invention, the concentrationof zinc cations preferably is at least, with increasing preference inthe order given, 0.010, 0.020, 0.030, 0.040, 0.045, or 0.049% andindependently preferably is not more than, with increasing preference inthe order given, 2.0, 1.5, 1.2, 1.0, 0.80, 0.70, 0.60, 0.55, 0.50, 0.45,0.40, 0.36, or 0.33%. In the first of two alternative especiallypreferred embodiments of the invention, one in which the NCM cationsconcentration is higher than the zinc cations concentration: theconcentration of zinc cations additionally preferably is not greaterthan, with increasing preference in the order given, 0.20, 0.15, 0.10,0.08, or 0.06%; and, independently, the ratio of zinc cations to NCMcations preferably is at least, with increasing preference in the ordergiven, 0.03:1.00, 0.05:1.00, 0.07:1.00, 0.09:1.00, or 0.11:1.00 andindependently preferably is not more than, with increasing preference inthe order given, 0.9:1.00, 0.7:1.00, 0.5:1.00, 0.40:1.00, 0.35:1.00,0.30:1.00, 0.25:1.00, 0.20:1.00, or 0.15:1.00. In the second of thesetwo alternative especially preferred embodiments of the invention, onein which the concentration of zinc ions is greater than theconcentration of NCM ions: the concentration of zinc cationsadditionally preferably is at least, with increasing preference in theorder given, 0.075, 0.10, 0.15, 0.20, 0.23, 0.25, 0.27, 0.29, or 0.31percent; and, independently, the ratio of zinc cations to NCM cationspreferably is at least, with increasing preference in the order given,1.10:1.00, 1.20:1.00, 1.30:1.00, 1.35:1.00, 1.40:1.00, 1.45:1.00,1.50:1.00, 1.55:1.00, or 1.58:1.00 and independently preferably is notmore than, with increasing preference in the order given, 7:1.00,5:1.00, 3.0:1.00, 2.7:1.00, 2.5:1.00, 2.3:1.00, 2.1:1.00, 1.9:1.00, or1.7:1.00.

Component (D) of iron cations is preferably sourced to a phosphatingcomposition according to the invention by a source of iron(III) ions,most preferably ferric nitrate although other water-soluble sources offerric ions may be used. The solubilities of ferric phosphate and offerric hydroxide are rather low in the presence of preferred amounts ofother constituents of a preferred phosphating composition according tothis invention, and it is in certain embodiments of the inventionpreferred to maintain the dissolved iron(III) cations at theirsaturation value by supplying an excess of ferric salt, most of whichremains undissolved unless and until some of the dissolved ferric ionsare removed from the composition by drag-out, precipitation as sludge,or the like. It should be noted that the solubilities of ferric saltsare affected by pH. At relatively low pH levels (high acidity) such asare typically present in the concentrate compositions of the presentinvention (replenisher or make-up), the ferric salt will generally bemore soluble than at higher pH levels. Precipitation of a portion of theferric salt dissolved in a replenisher or make-up concentrate will thuscommonly be observed when the concentrate is diluted in the workingphosphating composition.

The concentration of dissolved iron cations in a working phosphatingcomposition according to the invention preferably is at least, withincreasing preference in the order given, 40, 60, 80, or 100% of itssaturation level, which is believed to correspond to about 10 parts ofdissolved iron per million parts by weight of total phosphatingcomposition (this unit of concentration being freely used hereinafterfor any constituent of a phosphating composition and being hereinafterusually abbreviated as “ppm”). In order to assure maintenance of themost preferred fully saturated concentration of dissolved iron cations,it is preferred to provide to a phosphating composition according to theinvention an amount of total ferric salt that contains at least, withincreasing preference in the order given, 20, 30, 40, 50, or 60 ppm ofiron cations.

In at least certain embodiments of the invention, however, it may bedesirable to limit the amount of total ferric salt provided to thephosphating composition. At very high levels of total ferric salt,excessive sludging and/or scaling may take place. For this reason, itmay be advantageous to provide to the phosphating composition an amountof total ferric salt that contains not more than, with increasingpreference in the order given, 700, 600, 500, 400, 200 or 100 ppm ofiron cations.

Optional component (E) of conversion coating accelerator preferably ispresent in a composition according to the invention, because withoutthis component the coating formation rate usually is slower than isdesired. The accelerator when present in a working composition accordingto the invention preferably is selected from the group consisting of:0.3 to 4 parts of chlorate ions per thousand parts of total phosphatingcomposition, this unit of concentration being freely used hereinafterfor any constituent of the composition and being hereinafter usuallyabbreviated as “ppt”; 0.01 to 0.2 ppt of nitrite ions; 0.05 to 2 ppt ofm-nitrobenzene sulfonate ions; 0.05 to 2 ppt of m-nitrobenzoate ions;0.05 to 2 ppt of p-nitrophenol; 0.005 to 0.15 ppt of hydrogen peroxidein free or bound form; 0.1 to 10 ppt of hydroxylamine in free or boundform; 0.1 to 10 ppt of a reducing sugar; and 1 to 30 ppt of nitrateions. Nitrate ions are preferred within this group and are mostpreferably used without any of the other accelerators in this group.Nitrate ions are preferably sourced to the composition by at least oneof nitric acid and its salts. When nitrate ions are present in a workingcomposition according to the invention, their concentration morepreferably is at least, with increasing preference in the order given,1.5, 2.0, 2.5, 3.0, 3.3, 3.6, 3.9, 4.1, or 4.3 ppt and independentlypreferably is not more than, with increasing preference in the ordergiven, 25, 20, 17, 15, 13, 11, or 9.0 ppt. (If the concentration ofnitrate is too high, the danger of emissions of noxious oxides ofnitrogen from the phosphating composition is increased.)

The presence of optional component (F) of dissolved fluoride in acomposition according to the invention is also preferred, becausewithout it the danger of forming the small surface blemishes known inart as “white specking”, “seediness”, or the like is increased whenphosphating zinciferous surfaces, and there is also less likelihood ofobtaining the most desired crystal morphology. More preferably, thisfluoride is sourced to the composition in two differing forms:“uncomplexed fluoride” supplied by hydrofluoric acid and/or one of itssalts (which may be partially or totally neutralized); and “complexedfluoride” supplied to the composition by at least one of the acids HBF₄,H₂SiF₆, H₂TiF₆, H₂ZrF₆, and H₂HfF₆, and their salts (which also may bepartially or totally neutralized). Among this group, H₂SiF₆ and itssalts are most preferred, the acid itself being usually preferred foreconomy and ready commercial availability.

When both uncomplexed and complexed fluorides are present in a workingphosphating composition according to the invention and the concentrationof NCM in the phosphating composition is greater than the concentrationof zinc measured in the same mass-based units: the concentration ofuncomplexed fluoride in the phosphating composition preferably is atleast, with increasing preference in the order given, 0.02, 0.04, 0.06,0.08, 0.10, 0.12, 0.14, or 0.16 ppt and independently preferably is notmore than, with increasing preference in the order given, 2.0, 1.5, 1.0,0.8, 0.6, 0.40, 0.35, 0.30, 0.25, 0.23, 0.21, 0.19, or 0.17 ppt;independently, the concentration of complexed fluoride in thephosphating composition preferably is at least, with increasingpreference in the order given, 0.04, 0.08, 0.12, 0.16, 0.20, 0.24, 0.28,0.31, 0.33, 0.35, or 0.37 ppt and independently preferably is not morethan, with increasing preference in the order given, 4.5, 3.5, 2.5, 2.0,1.5, 1.0, 0.90, 0.80, 0.70, 0.60, 0.50, 0.45, or 0.40 ppt; and,independently, the ratio of uncomplexed fluoride to complexed fluoridepreferably is at least, with increasing preference in the order given,0.05:1.00, 0.10:1.00, 0.15:1.00, 0.20:1.00, 0.25:1.00, 0.30:1.00,0.35:1.00, 0.39:1.00, 0.41:1.00, or 0.43:1.00 and independentlypreferably is not more than, with increasing preference in the ordergiven, 4:1.00, 2.0:1.00, 1.5:1.00, 1.00:1.00, 0.80:1.00, 0.70:1.00,0.65:1.00, 0.60:1.00, 0.55:1.00, 0.50:1.00, 0.48:1.00, 0.46:1.00, or0.44:1.00.

When both uncomplexed and complexed fluorides are present in a workingphosphating composition according to the invention and the concentrationof NCM in the phosphating composition is less than or equal to theconcentration of zinc measured in the same mass-based units: theconcentration of complexed fluoride in the phosphating compositionpreferably is at least, with increasing preference in the order given,0.25, 0.50, 1.0, 1.5, 1.8, 2.0, 2.2, or 2.4 ppt and independentlypreferably is not more than, with increasing preference in the ordergiven, 20, 15, 10.0, 7.0, 5.0, 4.0, 3.5, 3.2, 2.9, 2.7, or 2.5 ppt;independently, the concentration of uncomplexed fluoride in thephosphating composition preferably is at least, with increasingpreference in the order given, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35,0.40, 0.45, 0.50, 0.54, 0.57, or 0.59 ppt and independently preferablyis not more than, with increasing preference in the order given, 7.0,6.0, 5.0, 4.5, 3.5, 2.5, 2.0, 1.5, 1.00, 0.90, 0.80, 0.70, 0.65, or 0.60ppt; and, independently, the ratio of uncomplexed fluoride to complexedfluoride preferably is at least, with increasing preference in the ordergiven, 0.02:1.00, 0.04:1.00, 0.06:1.00, 0.08:1.00, 0.10:1.00, 0.12:1.00,0.14:1.00, 0.16:1.00, 0.18:1.00, 0.20:1.00, 0.22:1.00, or 0.24:1.00 andindependently preferably is not more than, with increasing preference inthe order given, 2.0:1.00, 1.5:1.00, 1.00:1.00, 0.80:1.00, 0.50:1.00,0.45:1.00, 0.40:1.00, 0.35:1.00, 0.32:1.00, 0.29:1.00, 0.27:1.00, or0.25:1.00.

If a phosphating composition according to the invention contains eitherfluoride only in uncomplexed form or fluoride only in complexed form,then: if the NCM concentration is greater than the zinc concentration inthe phosphating composition, the total fluoride content of thecomposition preferably is at least, with increasing preference in theorder given, 0.10, 0.20, 0.30, 0.40, or 0.50 ppt and independentlypreferably is not more than, 5, 3, 2.0, 1.0, 0.8, or 0.6 ppt; but if theNCM concentration is less than or equal to the zinc concentration in thecomposition, the total fluoride content of the composition preferably isat least, with increasing preference in the order given, 0.5, 1.0, 1.5,2.0, 2.5, or 2.9 ppt and independently preferably is, with increasingpreference in the order given, not more than 20, 15, 10, 7, 5, or 3.1ppt.

Independently of other preferences, if a phosphating compositionaccording to the invention contains dissolved fluoride of any type, theratio of the total dissolved fluoride concentration to the dissolvedzinc cations concentration, both measured in the same mass-based units,preferably is at least, with increasing preference in the order given,0.2:1.00, 0.4:1.00, 0.6:1.00, 0.80:1.00, 0.87:1.00, or 0.92:1.00 andindependently preferably is not more than, with increasing preference inthe order given, 5:1.00, 3:1.00, 2.0:1.00, 1.8:1.00, 1.6:1.00, 1.4:1.00,1.20:1.00, or 1.10:1.00.

A phosphating composition according to this invention is necessarilyacidic. Its acidity is preferably measured for control and optimizationby two characteristics familiar in the art as “points” of Free Acid(hereinafter usually abbreviated as “FA”) and of Total Acid (hereinafterusually abbreviated as “TA”). Either of these values is measured bytitrating a 10.0 milliliter sample of the composition with 0.100 Nstrong alkali. If FA is to be determined, the titration is to an endpoint of pH 3.8 as measured by a pH meter or an indicator such asbromcresol green or bromthymol blue, while if TA is to be determined,the titration is to an end point of pH 8.0 as measured by a pH meter oran indicator such as phenolphthalein. In either instance, the value inpoints is defined as equal to the number of milliliters of the titrantrequired to reach the end point.

A working phosphating composition according to this invention preferablyhas an FA value that is at least, with increasing preference in theorder given, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7 or 1.9 pointsand independently preferably is not more than, with increasingpreference in the order given, 10, 8, 6.0, 5.0, 4.5, 4.0, 3.7, 3.5, 3.3,or 3.1 points. Also and independently, a working phosphating compositionaccording to the invention preferably has a TA value that is at least,with increasing preference in the order given, 10, 13, 16, 19, 22, 25,or 27 points and independently preferably is not more than, withincreasing preference in the order given, not more than, with increasingpreference in the order given, 50, 45, 40, 38, 36, or 34 points. Ifeither the FA or the TA value is too low, the phosphating coatingformation will be lower than is usually desired, while if either valueis too high there may be excessive dissolution of the substrate and/orsuboptimal crystal morphology in the coating formed. Ordinarily, the FAand TA values can be brought within a preferred range by use ofappropriate amounts of acidic sources of phosphate, nitrate, and/orcomplexed fluoride and basic sources of zinc and/or NCM, but if needed,optional component (G) preferably is used to bring the compositionwithin a preferred range of both TA and FA. Alkali metal hydroxides,carbonates, and/or oxides are preferably used for this purpose ifalkalinity is needed, and phosphoric acid and/or nitric acid ispreferably used if acidity is needed.

Optional component (H) of sludge conditioner is not always needed in acomposition according to the invention and therefore is preferablyomitted in such instances. However, in many instances, at least one suchconditioner may be advantageously used, in order to make separation andcollection of any sludge that forms easier. In any such instances,suitable material for these purposes can be readily selected by thoseskilled in the art. Preferred sludge conditioners are shown in theexamples below.

For various reasons, almost always including at least a cost saving fromelimination of an unnecessary ingredient, it is preferred that acomposition according to this invention should be largely free fromvarious materials often used in prior art compositions. In particular,compositions according to this invention in most instances preferably donot contain, with increasing preference in the order given, and withindependent preference for each component named, more than 5, 4, 3, 2,1, 0.5, 0.25, 0.12, 0.06, 0.03, 0.015, 0.007, 0.003, 0.001, 0.0005,0.0002, or 0.0001% of each of (i) dissolved calcium cations, (ii)dissolved copper cations, (iii) dissolved aluminum, and (iv) dissolvedchromium in any chemical form.

Preferred concentrations have been specified above for workingcompositions according to the invention, but another embodiment of theinvention is make-up concentrate compositions that can be diluted withwater only to produce a working composition, and the concentration ofingredients other than water in such a concentrate compositionpreferably is as high as possible without resulting in instability ofthe concentrate during storage, in order to minimize the cost ofshipping water from a concentrate manufacturer to an end user, who canalmost always provide water more cheaply at the point of use.

More particularly, in a concentrate composition according to thisinvention, the concentration of each ingredient other than waterpreferably is at least, with increasing preference in the order given,1.5, 2.0, 2.5, 3.0, 3.5, 4.0 or times as great as the preferred minimumamounts specified above for working compositions according to theinvention. In addition to the concentrations recited above, a make-upconcentrate preferably has the same ratios between various ingredientsas are specified for working compositions above.

A phosphating composition according to the invention is preferablymaintained while coating a metal substrate in a process according to theinvention at a temperature that is at least, with increasing preferencein the order given, 30, 40, 50, 55, 60, 62, 64, 66, or 68° C. andindependently preferably is not more than, with increasing preference inthe order given, 95, 90, 85, 81, 79, or 77° C.

The specific areal density (also often called “add-on weight [or mass]”)of a phosphate coating formed according to this invention preferably isat least, with increasing preference in the order given, 0.3, 0.6, 0.8,1.0, 1.2, 1.4, or 1.6 grams of dried coating per square meter ofsubstrate coated, this unit of coating weight being hereinafter usuallyabbreviated as “g/m²”, and independently preferably is not more than,with increasing preference in the order given, 10, 8, 6, 5.0, 4.5, 4.0,or 3.5 g/m². The phosphate conversion coating weight may be measured bystripping the conversion coating in a solution of chromic acid in wateras generally known in the art.

Before treatment according to the invention, metal substrate surfacespreferably are conventionally cleaned, rinsed, and “conditioned” with aJernstedt salt or an at least similarly effective treatment, all in amanner well known in the art for any particular type of substrate; andafter a treatment according to the invention the composition accordingto the invention generally should be rinsed off the surface coatedbefore drying.

This invention is particularly advantageously, and therefore preferably,used on zinciferous metal substrates, such as galvanized steel of allkinds and zinc-magnesium and zinc-aluminum alloys, or more generally anymetal alloy surface that is at least 55% zinc, and on such substratesthere are two particularly preferred established areas of commercialoperation in which this invention is especially advantageous and towhich it is therefore highly preferably applied.

In the first of these areas:

-   -   the phosphating composition used:        -   contains at least, with increasing preference in the order            given, 2.5, 3.0, 3.3, 3.6, 3.9, 4.1, 4.3, or 4.5 ppt of NCM            cations; and        -   contains NMC and zinc cations in a ratio of zinc to NMC that            preferably is at least, with increasing preference in the            order given, 0.03:1.00, 0.05:1.00, 0.07:1.00, 0.09:1.00, or            0.11:1.00 and independently preferably is not more than,            with increasing preference in the order given, 0.9:1.00,            0.7:1.00, 0.5:1.00, 0.40:1.00, 0.35:1.00, 0.30:1.00,            0.25:1.00, 0.20:1.00, or 0.15:1.00; and    -   the phosphating composition is:        -   in contact during its use in phosphating with at least one            surface on which no phosphate coating or other solid coating            formation is desired; and        -   maintained during its use at a temperature that preferably            is at least, with increasing preference in the order given,            50, 55, 60, 62, 64, 66, or 68° C.            Under such conditions, the formation of scale on the metal            surfaces on which no coating is desired is usually a serious            problem in the absence of iron in the phosphating            composition.

In the second established area of commercial operation in which thisinvention is most particularly preferred (an area which is not at allnecessarily exclusive of the first), the characteristic feature is avery rapid movement of the substrate through the phosphating compositionduring the phosphating process, a common condition in high speedtreatment of coils. When the relative speed of the substrate through thephosphating composition exceeds, with increasing preference in the ordergiven, 100, 125, 150, 160, 165, 170, 175, 180, or 185 meters per minute(this unit of speed being hereinafter usually abbreviated as “m/min”),it has surprisingly been found that dissolution of zinc from the surfaceof the substrate, which can normally be relied on to provide asufficient amount of zinc to compensate for the amount consumed as zincphosphate and make it unnecessary to add zinc in any replenisher for thephosphating composition, is often not effective for this purpose. Thisis severely limiting, because in prior art practice with phosphatingcompositions that did not contain dissolved iron cations but wereotherwise similar to those according to this invention, it hassurprisingly been found that adding a conventional zinc containingreplenisher is ineffective, inasmuch as most or all of the zinc contentof the replenisher added is rapidly precipitated as sludge. The presenceof iron in a composition according to the invention very greatly reducesthe amount of sludge formed by adding a replenisher that contains asubstantial concentration of zinc, particularly if the replenisheritself also contains dissolved iron cations.

Furthermore, in prior art practice with phosphating compositions similarto those of this invention except for the absence of iron in the priorart compositions, it has surprisingly been found that a high speed ofthe substrate through the phosphating composition resulted in a crystalmorphology in the coating formed that had inferior protective value,compared with a coating formed on the same substrate with the samephosphating when the motion of the substrate through the phosphatingcomposition was lower. This adverse effect also can be eliminated in aprocess according to this invention.

In any phosphating process according to this invention, as with all oralmost all other known phosphating processes, if the initially preparedphosphating composition is to be used for a long period, it is preferredto maintain the effectiveness of the process by adding a suitablereplenisher to compensate for any changes in the concentrations ofingredients in the initially prepared phosphating composition that occuras a result of using the phosphating composition. The optimumcharacteristics of a replenisher composition often depend on the natureof the substrate being coated and the relative speed of motion betweenthe phosphating composition and the substrate being phosphated. For thesecond of the two established areas of commercial operation in whichthis invention is most particularly preferred as noted above, apreferred replenisher composition preferably comprises water and thefollowing concentrations of the following other components:

-   (R2A) a concentration of dissolved phosphate anions that is at    least, with increasing preference in the order given, 15, 17, 19,    21, 23, 25, or 27% and independently preferably is not more than,    with increasing preference in the order given, 50, 45, 40, 37, 34,    32, 30, or 28%;-   (R2B) a concentration of dissolved NCM cations that is at least,    with increasing preference in the order given, 1.2, 1.4, 1.6, or    1.8% and independently preferably is not more than, with increasing    preference in the order given, 5.0, 4.0, 3.0, 2.5, 2.3, 2.1, or    1.9%;-   (R2C) a concentration of dissolved zinc cations that is at least,    with increasing preference in the order given, 4.0, 4.2, 4.4, 4.6,    4.8, 5.0, or 5.2% and independently preferably is not more than,    with increasing preference in the order given, 15, 12, 10, 8.0, 7.0,    6.0, or 5.5%; and-   (R2D) a concentration of dissolved iron cations that is at least,    with increasing preference in the order given, 0.02, 0.04, 0.06,    0.08, or 0.10%.    Optionally, one or more of undissolved iron cations and the    following concentrations of the following components may also be    present:-   (R2E) a concentration of nitrate ions that is at least, with    increasing preference in the order given, 5.0, 5.2, 5.4, 5.6, 5.8,    6.0, or 6.2% and independently preferably is not more than, with    increasing preference in the order given, 12, 10, 9.0, 8.0, 7.5,    7.0, 6.8, 6.6, or 6.4 percent;-   (R2F) a concentration of dissolved uncomplexed fluoride ions that is    at least, with increasing preference in the order given, 0.05, 0.10,    0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, or 0.58    percent and independently preferably is not more than, with    increasing preference in the order given, 1.5, 1.2, 1.0, 0.90, 0.80,    0.70, 0.65, or 0.62 percent;-   (R2G) surfactant that is not part of any of components (R2A) through-   (R2F) as recited immediately above; and-   (R2H) sludge conditioner that is not part of any of components (R2A)    through (R2G) as recited immediately above.    Preferred surfactant(s) and sludge conditioners are described in the    working examples.

For the first of the two established areas of commercial operation inwhich this invention is most particularly preferred as noted above, ifthe relative motion between the substrate being phosphated and thephosphating composition during phosphating is not as much as 100 metersper minute, a particularly preferred replenisher composition preferablycomprises water and the following concentrations of the following othercomponents:

-   (R1A) a concentration of dissolved phosphate anions that is at    least, with increasing preference in the order given, 13, 15, 17,    19, 21, 23, or 25 percent and independently preferably is not more    than, with increasing preference in the order given, 50, 45, 40, 37,    34, 32, 30, 28, or 26 percent;-   (R2B) a concentration of dissolved NCM cations that is at least,    with increasing preference in the order given, 4.2, 4.4, 4.6, or    4.8% and independently preferably is not more than, with increasing    preference in the order given, 8.0, 7.0, 6.0, 5.5, 5.3, 5.1, or    4.9%;-   (R2C) a concentration of dissolved zinc cations that is at least,    with increasing preference in the order given, 0.50, 0.60, 0.70,    0.80, 0.90, 1.00, or 1.06 percent and independently preferably is    not more than, with increasing preference in the order given, 4.0,    3.0, 2.5, 2.0, 1.7, 1.5, 1.3, or 1.1 percent; and-   (R2D) a concentration of dissolved iron cations that is at least,    with increasing preference in the order given, 0.02, 0.04, 0.06,    0.08, or 0.10%.    Optionally, one or more of undissolved iron cations and the    following concentrations of the following components may also be    present:-   (R2E) a concentration of nitrate ions that is at least, with    increasing preference in the order given, 3.0, 3.5, 3.7, 3.9, 4.1,    4.3, 4.5, or 4.7% and independently preferably is not more than,    with increasing preference in the order given, 10, 8.0, 7.0, 6.5,    6.0, 5.7, 5.4, 5.2, 5.0, or 4.8 percent;-   (R2F) a concentration of dissolved uncomplexed fluoride ions that is    at least, with increasing preference in the order given, 0.05, 0.10,    0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.42, 0.44, 0.46, or 0.48    percent and independently preferably is not more than, with    increasing preference in the order given, 1.2, 1.0, 0.90, 0.80,    0.70, 0.60, 0.55, or 0.50 percent;-   (R2G) surfactant that is not part of any of components (R2A) through    (R2F) as recited immediately above; and-   (R2H) sludge conditioner that is not part of any of components (R2A)    through (R2G) as recited immediately above.    Preferred surfactant(s) and sludge conditioners are described in the    working examples.

The practice of this invention may be further appreciated byconsideration of the following, non-limiting, working examples, and thebenefits of the invention may be further appreciated by reference to thecomparison examples.

EXAMPLE AND COMPARISON EXAMPLE 1

In these tests, both working phosphating compositions were made from aconcentrate with the ingredients shown in Table 1 below. The workingcompositions each contained 425 milliliters of this concentrate and 42grams of sodium carbonate in a total volume of 6.0 liters. Example 1also contained 4 grams of ferric nitrate nonahydrate crystals, but thisingredient was omitted from Comparison Example 1, which was otherwiseidentical to Example 1 in concentrations of ingredients other thanwater. Both working phosphating compositions had FA values of 2.5. TheTA value was 31.1 for Example 1 and 30.9 for Comparison Example 1. Eachworking composition was heated with one of two substantially identicalheating elements with a surface of Type 316 stainless steel exposed tothe working composition, which was maintained at 71″ 5 EC whileconventionally cleaned and conditioned galvanized steel test panels werephosphated by immersion for 5 seconds each. The appearance of thephosphated galvanized steel surfaces from Example 1 and ComparisonExample 1 was substantially identical in scanning electron micrographsat 1000 diameters magnification. However, after five hours of use, thesurfaces of the two immersion heaters were very different. The heater inExample 1 according to the

TABLE 1 Concentration, as % of the Total Composition, for the IngredientIngredient Shown at Left: 75% Solution of H₃PO₄ in water 21.4 Zinc Oxide0.90 Solution in water of nickel nitrate that contains 40.7 13.7% nickeland 30% nitrate Solution in water of nickel phosphate that contains 8.98.1% nickel and 37% phosphate 25% Solution of H₂SiF₆ in water 2.52 70%Solution of HF in water 0.40 Additional water Balanceinvention had a powdery scale that was readily removed by brushing,while the heater in Comparison Example 1 was covered with a tightlyadherent solid scale. About 3.5 grams of this solid scale was removedwith considerable difficulty from the heater in Comparison Example 1,while only about 0.7 grams of scale could be removed from the heater inExample 1.

A preferred replenisher for use with a high nickel-low zinc phosphatingcomposition as used in Example 1 contains the ingredients shown in Table2 below.

EXAMPLE 2 AND COMPARISON EXAMPLES 2.1 AND 2.2

In all of these examples, the substrate was also conventionally cleanedand conditioned galvanized steel, but in these examples the steel waspassed rapidly through the phosphating composition rather than beingimmersed in it. In both the Comparison Examples, the phosphatingcomposition contained the ingredients shown in Table 3 below. InComparison Example 2.1, the phosphating composition was replenished witha conventional replenisher that did not contain zinc or iron, and thespeed of the substrate through the phosphating composition was varied. Aminimum coating weight of 1.5 g/m² is required for this operation andwas readily achieved at substrate speeds up to 182 m/min. However, whenthe speed was raised to 199 m/min, satisfactory coating weights couldnot be maintained.

In Comparison Example 2.2, it was attempted to restore satisfactorycoating characteristics by adding a substantial concentration of zinc tothe replenisher previously used. This attempt was unsuccessful. As soonas the replenisher began to be added, the phosphating composition becameturbid and eventually obvious sludging began.

TABLE 2 Concentration, as % of the Total Composition, for the IngredientIngredient Shown at Left: 75% Solution of H₃PO₄ in water 29.3 Zinc Oxide1.30 Solution in water of nickel nitrate that contains 15.9 13.7% nickeland 30% nitrate Solution in water of nickel phosphate that contains 8.98.1% nickel and 37% phosphate Solid anhydrous NaH₂PO₄ 3.0 35% Solutionof HF in water 1.46 Solid Fe(NO₃)₃ •9H₂O 0.76 Additional water Balance

TABLE 3 Concentration, as % of the Total Composition, for the IngredientIngredient Shown at Left: Phosphate anions 9.2 Zinc cations 3.2 Nickelcations 2.0 Nitrate anions 4.4 Complex fluoride from H₂SiF₆ 2.4Uncomplexed fluoride from HF 0.59 Additional water BalanceThe coating characteristics did not improve, presumably becausesubstantially all of the zinc cations added in the replenisher wereprecipitated as zinc phosphate.

In Example 2 according to the invention, a phosphating composition wasused that contained the same ingredients for Comparison Example 1 exceptthat 0.062 percent of iron cations was added to the composition asferric nitrate nonahydrate, not all of which dissolved. The replenisherused had a composition including iron and zinc, as shown in full inTable 4 below. With these operating conditions, required coating weightsand other coating characteristics were easily achieved for a period oftwelve hours at a substrate speed of 199 m/min, and little or noturbidity and/or sludge formation was observed. The xanthan gum, urea,and sulfonate salt present in this composition are all sludge modifiers.

TABLE 4 Concentration, as % of the Total Composition, for the IngredientIngredient Shown at Left: 75% Solution of H₃PO₄ in water 37.5 Zinc Oxide6.5 Solution in water of nickel nitrate that contains 13.1 13.7% nickeland 30% nitrate 70% Solution in water of nitric acid 3.5 35% Solution ofHF in water 1.8 Solid Fe(NO₃)₃•9H₂O 0.76 Xanthan gum 0.10 Prilled urea0.05 Sodium 2-ethylhexyl sulfonate 0.08 Additional water Balance

EXAMPLES 3, 3.1 AND 3.2

To further demonstrate the influence of the total amount of ferric salton sludge and scale formation, three phosphating baths were preparedusing varying iron levels as described in Table 5. The baths were builtup using BONDERITE 1421 make up (available from the Surface Technologiesdivision of Henkel Corporation, Madison Heights, Mich., U.S.A.) anddiffering amounts of ferric nitrate nonahydrate. Hot dipped G70galvanized steel test panels (supplied by ACT) were cleaned with PARCO1200 cleaner (available from the Surface Technologies division of HenkelCorporation) (14 point, 60° C., 10 seconds), then rinsed with hot water(10 seconds), and treated with PARCOLENE AT conditioner (available fromthe Surface Technologies division of Henkel Corporation) at 28° C. priorto immersion in the phosphating baths (77-80° C., 5 sec.). Coatingweights were measured by stripping using ammonium dichromate, inaccordance with conventional practice. Scaling and sludging wereevaluated by visual inspection of the reaction vessel and the amount ofscale deposited on the immersion heating device over the course of thephosphating operation (approximately 6 hours). At 75 ppm and 7.5 ppm Fe(III) (Examples 3 and 3.2, respectively), acceptable levels of scalingand sludging were observed. Severe sludge and scale formation occurredwhen operating at 750 ppm Fe (III) (Example 3.1). The phosphating bathsfor Examples 3 and 3.2 had precipitate present, which suggests that thebaths were saturated with ferric salt. Although Example 3.2 (7.5 ppm Fe(III)) gave optimum results (no sludging, minimal scaling), incommercial operation it would be preferable to operate at a somewhathigher Fe (III) level due to the problems associated with trying toprecisely maintain a very low concentration of Fe (III), as a relativelyminor decrease in the Fe (III) level (e.g., where the level approaches 0ppm) could lead to severe sludging and scaling problems.

TABLE 5 Coating Weight, Example Fe (III), ppm g/m² Sludge Scale 3 751.98 Minimal Minimal 3.1 750 1.95 Pronounced Pronounced 3.2 7.5 2.07None Minimal

1. An improved phosphating operation wherein metal substrates are eitherA. contacted in a bath A with a working phosphating composition Acomprised of water, dissolved phosphate anions, dissolved NCM cations,and dissolved zinc cations, wherein said bath A additionally contains atleast one piece of process equipment having a surface, and wherein arelatively hard, adherent, and difficult to remove scale forms on saidsurface when said surface is in contact with said working phosphatingcomposition A for an extended period of time; or B. continually passedat a high rate of speed through a bath B containing a workingphosphating composition B comprised of water, dissolved phosphateanions, dissolved NCM cations and dissolved zinc cations, wherein areplenisher composition comprised of zinc cations is periodically addedto said working phosphating composition and wherein sludge forms in bathB following such addition of the replenisher composition; theimprovement comprising said working phosphating composition A or saidworking phosphating composition B comprising a concentration ofdissolved zinc cations that is not greater than 0.08 wt. %, wherein theratio of dissolved zinc cations to dissolved NCM cations is not morethan 0.5:1.00, and maintaining a level of dissolved ferric cations insaid working phosphating composition A or said working phosphatingcomposition B which is effective to either reduce the amount of scaleforming on said surface or reduce the amount of sludge forming in bath Bin said working phosphating composition A or working phosphatingcomposition B, wherein working phosphating composition A or workingphosphating composition B is maintained at a temperature of at least 66°C.
 2. The phosphating operation of claim 1 wherein said high rate ofspeed is in excess of 100 meters per minute.
 3. The phosphatingoperation of claim 1 wherein working phosphating composition A orworking phosphating composition B is additionally comprised of at leastone phosphating accelerator.
 4. The phosphating operation of claim 1wherein working phosphating composition A or working phosphatingcomposition B is additionally comprised of dissolved fluoride ions. 5.The phosphating operation of claim 1 wherein working phosphatingcomposition A or working phosphating composition B is additionallycomprised of at least one acidity adjustment agent.
 6. The phosphatingoperation of claim 1 wherein working phosphating composition A orworking phosphating composition B is additionally comprised of at leastone sludge conditioner.
 7. The phosphating operation of claim 1 whereinworking phosphating composition A or working phosphating composition Bis comprised of from 0.2 to 20% dissolved phosphate anions.
 8. Thephosphating operation of claim 1 wherein working phosphating compositionA or working phosphating composition B is comprised of 0.4 to 1.4%dissolved NCM cations.
 9. The phosphating operation of claim 1 whereinworking phosphating composition A or working phosphating composition Bis comprised of a concentration of dissolved zinc cations that is notgreater than 0.06 wt. %.
 10. The phosphating operation of claim 1wherein the ratio of dissolved zinc cations to dissolved NCM cations inworking phosphating composition A or working phosphating composition Bis at least 0.03:1.00 and not greater than 0.4:1.00.
 11. The phosphatingoperation of claim 1 wherein the ratio of dissolved zinc cations todissolved NCM cations in working phosphating composition A or workingphosphating composition B is at least 0.05:1.00 and not greater than0.3:1.00.
 12. The phosphating operation of claim 1 wherein theconcentration of dissolved ferric cations in the working phosphatingcomposition A or working phosphating composition B is maintained at alevel which is at least 40% of the saturation level for iron ions in theworking phosphating composition A or working phosphating composition B.13. The phosphating operation of claim 1 wherein an amount of totalferric salt is present in the working phosphating composition A orworking phosphating composition B that contains at least 20 ppm ironcations.
 14. The phosphating operation of claim 1 wherein workingphosphating composition A or working phosphating composition B has an FAvalue of from 0.1 to 10 points.
 15. The phosphating operation of claim 1wherein working phosphating composition A or working phosphatingcomposition B has a TA value of from 10 to 50 points.
 16. Thephosphating operation of claim 1 wherein working phosphating compositionA or working phosphating composition B is maintained at a temperaturethat is not more than 95° C.
 17. The phosphating operation of claim 1wherein said metal substrates are comprised of a material selected fromthe group consisting of galvanized steel, zinc magnesium alloys andzinc-aluminum alloys.
 18. The phosphating operation of claim 1 whereinworking phosphating composition A is comprised of at least 2.5 ppt ofNCM cations and has a ratio of zinc cations:NCM cations that is at least0.003:1.00 and not greater than 0.5:1.00 and is maintained at atemperature of at least 66° C.
 19. The phosphating operation of claim 1wherein said level of dissolved ferric ions in working phosphatingcomposition B is maintained by incorporating a ferric salt in saidreplenisher composition.
 20. The phosphating operation of claim 1wherein an amount of total ferric salt is present in the workingphosphating composition A or working phosphating composition B thatcontains no more than 400 ppm iron cations.
 21. The phosphatingoperation of claim 1 wherein said level of dissolved ferric cations isat least 4 ppm.
 22. The phosphating operation of claim 1 wherein saidlevel of dissolved ferric cations is at least 8 ppm.
 23. The phosphatingoperation of claim 1 wherein said level of dissolved ferric cations isat least 10 ppm.
 24. The phosphating operation of claim 1 wherein saidhigh rate of speed is in excess of 180 meters per minute.
 25. Thephosphating operation of claim 1 wherein the metal substrates arecontacted in the bath A with the working phosphating composition A andwherein said level of dissolved ferric cations in said workingphosphating composition A is effective to reduce the amount of solidscale forming on said surface.
 26. The phosphating operation of claim 25wherein said level of dissolved ferric cations in said workingphosphating composition A is effective to reduce the amount of solidscale forming on a surface of a heater that is in contact with saidworking phosphating composition A during said phosphating operation.